Performance of the LHD cryogenic system during cooling and excitation tests

Performance of th LUD cryogenic system in the first year's operation wits described making importance un tlte recovery process after the normal transition of the helical coils. During the excitation tests of the LHD superconducting coils up to 2.75 T, the normal zone propagation was observed in the helical coil and the emergency shutoff of the coil power supplies was cnrricd out. 2,700 I of liquid helium evaporated from the helical coils. The coils and the helium refrigerator were separated automatically and the helium refrigerator could keep its steady slat operation. After the pressure and flow rate of the recovery gas from the helical coils were settled down to the nurmnl state, the coils were connected to the helium refrigerator and the cooling was restarted, The system could return to the steady state in which coil excitation is enabling) by only three and a lialfhuiirs.